1. Field of the Invention
The present invention relates to a liquid crystal display device.
2. Description of the Related Art
In a horizontal electric field system (JP 2000-352713 A) which is an example of a display system of the liquid crystal display device, for the purpose of allowing a direction of a molecular axis of oriented liquid crystal molecules to rotate in a plane substantially parallel to substrates, a common electrode and pixel electrodes are disposed on one substrate, respective voltages are applied to the common electrode and the pixel electrodes, and electric field components substantially parallel to the substrates are used for display. The liquid crystal display device of the horizontal electric field system has advantages that a wide viewing angle can be obtained, and an image contrast can be improved.
In the related art liquid crystal display device of the horizontal electric field system, the horizontal electric field is generated between adjacent comb electrodes. Therefore, because a horizontal component of the electric field is small on the comb electrodes, a liquid crystal material cannot be sufficiently rotated.
FIG. 23 of JP 2012-220575 A discloses a configuration in which wall electrodes are arranged on both ends of one pixel. The respective wall electrodes are formed on both ends of one pixel, and one of the wall electrodes is each pixel electrode, and the other wall electrode is a common electrode. Also, a plane electrode is disposed for blocking an influence (signal wiring potential and a potential of an adjacent pixel) of a peripheral potential of the pixel.
As a result of evaluating the characteristic of the liquid crystal display device, it is found that an equipotential surface within one pixel is left-right asymmetric from a center of the pixel, and an orientation state of liquid crystal is also left-right asymmetric. The reason is because since the pixel electrode is surrounded by an influence of a potential around the pixel electrode, the equipotential surface is formed centered on each pixel electrode, and an electric field distribution in the vicinity of the pixel electrodes and an electric field distribution in the vicinity of the common electrode are different from each other. Also, an electric force line distribution is dense in the vicinity of the pixel electrodes and coarse in the vicinity of the common electrode, and an intense vertical electric field is generated on the plane electrode in the vicinity of the pixel electrode. For that reason, liquid crystal in the vicinity of each pixel electrode is tilted up, and the orientation state of liquid crystal is left-right asymmetric in the vicinity of the pixel electrode and the common electrode. A transmittance in a direction along which the liquid crystal in the vicinity of the pixel electrode rises up, that is, when obliquely viewing a display is lowered to degrade a viewing angle characteristic. In particular, the lowering of the transmittance is remarkable in a halftone.